POS0811 HIGH DIMENSIONAL CARTOGRAPHY OF LYMPHOCYTES USING SINGLE-CELL MASS CYTOMETRY DIFFERENTIATES SYSTEMIC LUPUS ERYTHEMATOSUS AND PRIMARY SJÖGREN`S SYNDROME
Authors: F. Szelinski, A. L. Stefanski, A. Glenzer, A. Frei, A. Lino, T. Dörner
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Autoimmune conditions such as primary Sjögren's syndrome (pSS) and systemic lupus erythematosus (SLE) share clinical and serological features characterized by IFN signature (1), autoantibody formation (2), post-activated phenotype (3) and chronic inflammation. Although the 2019 SLE EULAR/ACR classification criteria facilitate a more precise clinical discrimination between SLE and pSS (4), a better understanding of the distinct immunological patterns of both diseases is required for developing fine-tuned immune modulations as therapeutic interventions. <h3>Objectives</h3> In this study we aimed at characterizing and deep phenotyping of lymphocytes and innate immune cells of patients with SLE and pSS for a better differentiation and understanding of immunological abnormalities. <h3>Methods</h3> Peripheral PBMCs of patients with SLE (n=21) or pSS (n=13) as well as from healthy controls (HD, n=15) were isolated. PBMCs were stained with both a B and a T/innate panel and analyzed using mass cytometry. After manual pre-gating of CD19+, CD3+ and innate immune cells, unbiased clustering analysis was performed and visualized as UMAPs. Clusters were identified and subsequently annotated according to median expression of lineage markers. <h3>Results</h3> Altogether, we identified 13 clusters in the B cell, 12 cluster in the T cell and 13 clusters in the innate compartment with disease dependent variations in frequencies and marker expression. B cell abnormalities were characteristic of SLE while striking T cell abnormalities were more prominent in pSS. IgD- CD27- double negative (DN) B cell sub-clusters were increased in SLE. Among the DN subsets the frequency of the cluster that presented with a lower CD19 expression correlated with PB frequencies. A Comparison of activation markers revealed increased CD86 expression on various B cell clusters of patients with SLE. Further, a memory B cell cluster expressing IgA stood out by higher KI-67 and CD45RO expression. In pSS patients, PD1+ ICOS+ CD4+ T follicular helper cell, CD8 effector memory and terminal differentiated effector memory CD8 T cell clusters were expanded. Notably, checkpoint molecules ICOS, TIGIT and PD1 were upregulated on various T cell clusters. Finally, intermediated monocytes that express CD226 were reduced in SLE when compared to pSS. <h3>Conclusion</h3> High dimensional characterization of B, T and innate immune cells of patients with SLE or pSS illustrated immunological differences between diseases. SLE showed more B cell abnormalities while T cell alterations were more prominent in pSS consistent with distinct activation pathways driving these diseases. The immunologic abnormalities, distinct for pSS and SLE, might contribute to a better disease monitoring and selective treatment approaches. <h3>References</h3> [1]Rose T, Szelinski F, Lisney A, Reiter K, Fleischer SJ, Burmester GR, et al. SIGLEC1 is a biomarker of disease activity and indicates extraglandular manifestation in primary Sjögren's syndrome. RMD Open. 2016;2(2):e000292. [2]Andraos R, Ahmad A, Eriksson P, Dahlström Ö, Wirestam L, Dahle C, et al. Autoantibodies associated with systemic sclerosis in three autoimmune diseases imprinted by type I interferon gene dysregulation: a comparison across SLE, primary Sjögren's syndrome and systemic sclerosis. Lupus Science &amp;amp;amp; Medicine. 2022;9(1):e000732. [3]Weißenberg SY, Szelinski F, Schrezenmeier E, Stefanski AL, Wiedemann A, Rincon-Arevalo H, et al. Identification and Characterization of Post-activated B Cells in Systemic Autoimmune Diseases. Front Immunol. 2019;10:2136. [4]Assan F, Seror R, Mariette X, Nocturne G. New 2019 SLE EULAR/ACR classification criteria are valuable for distinguishing patients with SLE from patients with pSS. Annals of the Rheumatic Diseases. 2021;80(8):e122. <h3>Acknowledgements</h3> Dr. Sebastian Fuchs. <h3>Disclosure of Interests</h3> Franziska Szelinski: None declared, Ana-Luisa Stefanski: None declared, Annika Glenzer: None declared, Andreas Frei Employee of: Roche, Andreia Lino: None declared, Thomas Dörner Grant/research support from: Roche.